Phosphines, the phosphorous analogues of organic amines, constitute a class of highly important compounds with widespread industrial applicability within numerous areas. Tertiary phosphines are involved in a variety of extensively utilized chemical reactions, for instance the Wittig reaction, i.e. the conversion of a ketone or an aldehyde functionality into an olefin linkage, the Mitsunobu reaction for stereo-specific preparations of C—O, C—N, C—S, or C—C bonds from alcohol functionalities, the Staudinger reaction, i. e. conversion of azides to free amides, or the Apple reaction for stereo-specific transformation of alcohols to halides. Additionally, phosphines are utilized as ligands in homogenous catalysis.
Tertiary phosphines are commonly prepared through reduction of the corresponding phosphine oxides. Over the years, concomitantly with the realization that tertiary phosphines are highly versatile and useful compounds for various applications, numerous different processes for the preparation of these organophosphorous agents have been developed. However, virtually all chemical processes for preparing tertiary phosphines suffer from one or more disadvantages, relating to for instance cost, reagent handling, high reaction temperature intervals, severe purification requirements, or significant environmental impact, as well as the inherent complexity of the reaction system. Polymeric analogues of triphenyl-phosphine have, inter alia, been reported as a means to mitigate the problem with extensive purification, enabling simple filtration-based removal of the undesired product of a particular chemical reaction. However, despite being an elegant solution to the purification problem, issues associated with high reagent cost and substantial water requirements decrease the utility of said strategy.
An alternative approach for allegedly generating a relatively pure tertiary phosphine product, supposedly obtainable through an economically feasible route, is disclosed in U.S. Pat. No. 4,113,783, wherein triphenylphosphine oxide is reacted with a dialkylaluminium hydride followed by subsequent hydrolysis, in order to obtain the desired product. A similar approach is disclosed in U.S. Pat. No. 4,507,504, where the reducing agent is a trialkylaluminium/boron trihalide compound, again providing a purportedly inexpensive route to tertiary phosphines. Despite disclosing asserted inexpensive routes to tertiary phosphines, the environmental impact of essentially all tertiary phosphine producing reactions of the prior art is very high, inter alia as a result of the use of harsh reagents, high temperatures, and/or substantial amounts of solvents. Further, numerous teachings of the prior art relate to procedures with low susceptibility for industrial application, relatively often as an implication of a lack of scalability, or as a result of the use of harsh reagents, obstructing safe and environmentally feasible process development.